Nov. 14 (Bloomberg) -- Berkshire Hathaway Inc. reported a
stake in Exxon Mobil Corp. valued at about $3.7 billion as
Warren Buffett’s company disclosed its largest new holding since
adding International Business Machines Corp. in 2011.

Buffett’s company owned 40.1 million shares of Exxon on
Sept. 30, Omaha, Nebraska-based Berkshire said today in a
regulatory filing. The world’s biggest oil company by market
value closed at $93.22 today in New York. It rose to $93.90 in
extended trading at 5:14 p.m., after the filing.

Berkshire has benefited this year as its stock picks
rallied along with the broader market, affirming a strategy of
favoring equities instead of bonds amid near record-low interest
rates. Buffett has tracked Exxon and bought its stock in the
past, holding a stake in the Irving, Texas-based energy producer
as recently as 2011.

Exxon Mobil “is undervalued, in his opinion, and pretty
much being ignored by the market,” said David Kass, a professor
at the University of Maryland’s Robert H. Smith School of
Business who has taken students to meet Buffett in Omaha. “He
knows the company. He knows it well.”

About three-quarters of the Exxon holding was added in the
three months ended June 30, according to a separate filing
today. Berkshire requested confidential treatment in an August
filing listing its holdings at the end of the second quarter.
The U.S. Securities and Exchange Commission sometimes allows
companies to withhold information from the public to limit
copycat investing while they build or cut a position.

Efficient Explorer

Exxon, which traces its roots to the 1880s and John D.
Rockefeller’s Standard Oil Trust, is among the most-efficient
explorers among major international energy producers, spending
$19.27 to find the equivalent of a barrel of crude last year,
according to data compiled by Bloomberg.

That compared with $21.48 in per-barrel costs for Chevron
Corp., Exxon’s next-largest U.S. rival, and $22.66 for BP Plc.

Exxon boosted oil and natural-gas production by 1.5 percent
during the third quarter, reversing a two-year stretch of output
declines. Net income for the period dropped by 18 percent to
$7.87 billion as rising crude prices that benefited the
company’s oil-production business squeezed margins at Exxon’s
refineries.

Brent crude futures traded in London, the benchmark price
for more than half the world’s oil, have averaged $108.48 a
barrel this year. Although that’s down 2.9 percent from the 2012
average, it’s still almost twice as much as the 2001-2010
average, according to data compiled by Bloomberg.

Energy Wagers

Buffett, Berkshire’s chairman and chief executive officer
for more than four decades, has had successes and blunders
betting on energy. He booked profits in 2007 as he sold stock in
PetroChina Co. after the shares rose more than eightfold since
Berkshire’s $488 million investment in 2003.

In 2009, Berkshire posted its worst quarterly loss in at
least two decades, fueled by a charge on the decline of oil
producer ConocoPhillips. Buffett said he made a major mistake
investing in the company with oil prices near their peak.

Berkshire cut its stake in ConocoPhillips by 44 percent in
the three months ended Sept. 30 to 13.5 million shares, today’s
filing showed.

Buffett’s track record of compounding shareholders’ money
earned him a following among investors. Quarterly filings
listing Berkshire’s U.S. stock holdings are studied by mutual
funds and individuals looking for clues about his strategy.

Two years ago, Buffett disclosed he had spent more than $10
billion accumulating shares of IBM. Buffett calls Berkshire’s
investments in the computer-services company, Coca-Cola Co.,
Wells Fargo & Co. and American Express Co. his “big four.”
Each was valued at more than $10 billion at the end of
September.